Method and apparatus for combined stretch forming and die drawing



1967 s. M. DOLNEY ETAL 3,299,689

METHOD AND APPARATUS FOR COMBINED STRETCH FORMING AND DIE DRAWING FiledMay 18, 1964 6 Sheets-Sheet 1 L INVENTORS.

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METHOD AND APPARATUS FOR COMBINED STRETCH FORMING AND DIE DRAWING FiledMay 18, 1964 6 Sheets-Sheet 2 32 IM ENTORfi.

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S. M. DOLNEY ETAL METHOD AND APPARATUS FOR COMBINED STRETCH Jan. 24,1967 FORMING AND DIE DRAWING Filed May 18, 1964 6 Sheets-Sheet 4 IN\I'ENTORS OOO Qua

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METHOD AND APPARATUS FOR COMBINED STRETCH FORMING AND DIE DRAWING FiledMay 18, 1964 6 Sheets-Sheet 5 m VENTORS. J774/\/ 5V M. .004 NE) B05587A. MACKf/VZ/E s. M. DOLNEY ETAL 3,299,689 METHOD AND APPARATUS FORCOMBINED STRETCH Jan. 24, 1967 FORMING AND DIE DRAWING Filed May 18,1964 6 Sheets-Sheet 6 INVENTOR5. J'TANAEV M- 004m 205527 A. M C/(A/Z/ X4,4 77O/Q/VA K United States Patent Ofiice 3,299,689 Patented Jan. 24,1967 3,299,639 METHOD AND APPARATUS FOR COMBINED STRETCH FORMING AND DIEDRAWING Stanley .M. Dolney, Parana, and Robert A. Mackenzie,

Chagrin Falls, Ghio, assignors to The Cyril Bath Company, Cleveland,Ohio, a corporation of Ohio Filed May 18, 1964, Ser. No. 368,014 18Claims. (Cl. 72297) This invention relates to a method and apparatus forcombined stretch forming and die drawing of sheet material.

United States Letters Patent of Cyril 1. Bath, No. 2,961,- 028, issuedNovember 22, 1960, and No. 3,116,780, issued January 4, 1964, disclose amethod of combined stretch forming and die drawing and apparatustherefor.

As therein more fully described, sheet metal stock is formed bystretching it along one dimension into a range above its elastic limitso as to render the metal more readily formable. While the metal remainsin the more readily formable condition as a result of stretching, it isdrawn to final shape between conventional drawing dies. The tensioningis eifected along one dimension of the stock by gripping two oppositemargins of the stock in gripping heads and then moving the headsrelatively apart while leaving the other margins which extend along thetensioning dimension free to be pulled in laterally by the dies as thedies close.

In some instances, the metal is pulled in solely by the portions of thedies which draw the part of the blank that becomes the final article orpart after trimming. In others, the margins of the dies surrounding suchpart are provided with matching beads and grooves. These beads andgrooves become operative initially to gather or draw metal into the diesas the dies are closing. Near the end of the drawing operation, afterthe article is almost drawn to final shape, they place a yieldablerestraint on the already drawn in margins so that the remainder of themetal lying within the drawn in margins is drawn to a greater degreethan it would be in the absence of such restraint. This restraint,however, is imposed only by the dies themselves during their closure andnot by any hold down means operable independently of the closure of thedies or prior to the drawing of the metal by the cooperation of thedies. This method, with or without the beads, has proven highlyeffective for large numbers of shapes.

However, in some instances in which abrupt changes of contour orso-called sharp character lines are required for decoration or utility,improved results can be obtained by controlling the movement of thestock inwardly of the dies in a direction transversely of the tensioningdimension. This control can be effected by means which can be operatedindependently of the die movement and thereby initiate the restraintprior to any drawing by the coaction of the dies, or at any stage of dieclosure.

In accordance with the present invention, the metal stock is firstprestretched in one dimension into a range above the elastic limit so asto render the metal more readily formable by the dies, as described inthe above patents. Then, preferably before drawing the metal by thecoaction of the dies but while the stock is in the more readilyforma-ble condition, the margins of the stock extending along thetensioning dimension are engaged by hold down means which restrain andcontrol the movement of the margins inward-1y transversely of thetensioning dimension during the closure of the dies. The hold down meansare operable for gripping the margins independently of the die closureso that, if desired, the restraint can be initiated not only prior toany drawing by die closure, but also at any stage of drawing by thedies, and continued until the dies are fully closed.

For brevity in description, the dimension in which the sheet metal stockis stretched by the stretch forming units preparatory to die'closure arereferred to hereinafter in the description and claims as endwise, themargins gripped by the units are referred to as end margins, and themargins extending along the tensioning dimension are referred to aslateral margins. These terms are used whether the stock is longer orshorterin the dimension of tensioning than transversely thereof. t

For carrying out the present method a conventional double action pressis employed, as distinguished from the single action press disclosed inthe above patent. The stretch forming units may be carried by the pressdirectly, or by fastening them on one of the drawingdies, asillustrated.

Generally it is preferable to maintain tensioning by the stretch formingunits during die closure. In such a case, only the lateral margins ofthe stock are controlled by the hold down means, and the stretch unitsare used to control the pull in of the end margins gripped by thestretch units. In this instance, stretch units which app-1y yieldabletensioning force to the stock are employed, as they can be drawninwardly endwise by the stock with controlled yieldable resistanceduring die drawing.

On the other hand, in some instances, it is unnecessary to maintain thetension by the units during drawing. This is because once the metal istensioned above the elastic limit to render it more readily deformable,it remains in the more readily deformable condition for an instant.Accordingly, as soon as the metal is thus tensioned, its entireperipheral margin may be gripped immediately by the hold down means, andthe dies operated immediately to draw the metal While this more readilydeformable condition obtains and before work hardening. In such aninstance, the stretch forming units may be released from the metalbefore or after' gripping of the peripheral margin of the stock by thehold down means. This is possible because the press operation issutliciently rapid so that the more readily deformable condition of thestock exists at the time of die closure whether the gripping beads aremaintained in gripping relation thereto or not.

The restraint imposed on the lateral margins of the sheet is not usuallya total restraint, but instead a controlled restraint obtained byaffording some slippage of the stock margin gripped by the hold downmeans. This slippage is selected in accordance with requirements imposed by the shape of the particular article being formed, Only in usualcircumstances are the gripped lateral margins completely locked againstslippage and resultant movement inwardly of the die.

As mentioned, the stock is first stretched endwise by the stretchforming units before it is drawn by coaction of the dies, but it may bestretched by the units partially over the male die only, and thensubsequently restrained at the margins by the hold down means.

In either event, after the stock is thus rendered more readilydeformable prior to coaction of the dies, the press is operated to causethe hold down means to engage the selected margins of the stock underpredetermined pres sure while the stock remains, or is maintained, inthe more readily deformable condition.

Various specific objects and advantages of the invention will becomeapparent from the following description wherein reference is made to thedrawings, in which:

FIG. 1 is a front elevation of the combined die drawing and stretchforming press embodying the principles of the present invention;

FIG. 2 is a bottom plan view of the male die and the hold down meansshowing their relation in the press;

FIG. 3 is a top plan view of the female die with the stretch formingunits of the present invention in assembled 3 relation therewith asviewed from line 3-3 in FIG. 4, but with the male die lifted clear ofthe female die;

FIG. 4 is an enlarged fragmentary front elevation of the stretch formingunits and female die illustrated in FIG. 1, part of one of the stretchforming units being shown in vertical section for clearness inillustration;

FIG. 5 is an enlarged right end elevation of the female die and one ofthe stretch units mounted thereon;

FIG. 6 is a fragmentary enlarged cross sectional view taken on line 66in FIG. 1 and showing the hold down means and its manner of cooperationwith the female die;

FIG. 7 is a view similar to FIG. 2, showing a modification of the holddown means thereof;

FIG. 8 is a view similar to FIG. 3. illustrating a modified form of holddown surface on the female die;

FIG. 9 is a diagrammatic illustration of the hydraulic and electricalcontrol circuitry of the apparatus adapted for performing the method ofthe present invention automatically;

FIG. 10 is a fragmentary front elevation of the press such asillustrated in FIG. 1 with a modified form of the stretch unitincorporated therein;

FIG. 11 is a fragmentary top plan view of the female die and one of thestretch forming units illustrate-d in FIG. 10; and

-FIG. 12 is a fragmentary right end elevation of the press and one ofthe stretch forming units thereon.

Referring to the drawings, the present invention is shown as embodied ina conventional double action mechanical press-of the toggle operatedtype, its use with other types of mechanical presses'and hydraulicpresses being readily apparent from the illustrative example.

Referring first to FIG. 1, the press, indicated generally at 1,comprises abed 2 with upright frame members 3 disposed at opposite endsof the bed. The members 3 are connected at the top to a suitable crown 4which supports the driving mechanism of the rams of the press.

Mounted in suitable guideways 5 on the frame members 3 for reciprocationvertically is an outer or a hold down ram 6 generally in the form of arigid box-like frame which is open at the top and bottom. The peripheralbottom edge 7 is adapted to support a conventional hold down ring, aswill later be described.

Mounted within the ram 6 is a die carrying ram 10. The ram 10 hassuitable extensions 11 which operate in guideways 12 on the members 3and support the ram 10 for vertical movement relative to the ram 6. Thedie carrying ram 10 and hold down ram 6 are thus mounted for movement inparallel vertical paths independently of each other.

For driving the hold down ram 6 and die carrying ram 10, a suitablemotor 11 is mounted on the crown 4 and drives a flywheel 12. Theflywheel 12 carries a coaxial pinion 13 which, in turn, drives a gear14.- The gear 14 carries a coaxial pinion 15. The pinion 15 directlydrives one of two main driving gears 16 and, through an'idler gear 17,the other of the two main driving gears 16. The main driving gears 16carry coaxial pinions18, respectively, one of which drives one oftwodriving gears 19 and the other of which drives the other of the twodriving gears 19. The gears 19 carry eccentric crank pins 20 which areconnected by links 21, respectively, to the ram 10. Carried on theshafts of the gears 16, for rotation relative thereto, are cranks 22a ofconventional linkages 22, indicated in dotted lines The linkages aredriven by eccentrics 22b on the gears 19, and through cranks 22a andlinks 23, drive the ram 6 with conventional dwell at the bottom of itsstroke.

In operation of the press, the hold down ram 6 first moves to a bottomor seated position and there dwells. During the dwell, the ram 10continues moving downwardly so that its die engages and draws the stockto final shape, after which the hold down ram 6 retracts.

Adjustment devices 24 are provided between the links 21 and the holddown ram 6, and-adjustment devices are provided between the links 23 andthe ram 10. The adjustment devices 24 and 25 are for adjusting thevertical starting positions of the hold down ram 6 relative to the dieram 10 so that the seating of the hold down ring on' the ram 6 and themovement of the die to final position by the ram 10 can be adjusted withrelation to each other, depending upon the requirements of theparticular work to be formed.

The outer ram or hold down ram 6 carries at its lower end a hold downring 30 having an under surface for cooperation with suitable holdingsurfaces on the female die. In the form illustrated, the ram 10 carriesa male die 31. The press frame carries a bolster block 32 which, inturn, supports a female die 33. Generally, suitable elongated beads areprovided on the under side of the ring 30 for cooperation with suitablegrooves in the upwardly facing margin of the female die for gripping andcontrolling the pull in of the metal inwardly of the dies during thedrawing operation.

The structure thus far described is a conventional press which may bepurchased on the market, and of itself does not embody the presentinvention.

As described in the above patent, the metal is left free to be drawn intransversely of the dies except for such control as might be afforded byconfiguration in the cooperating faces or margins of the diesthemselves. There is no hold down means operable independently of thedies themselves for holding the lateral margins ofthe stock andcontrolling the degree to which the metal is permitted to be pulled inlaterally by closure of the dies.

In the present invention, the stretch forming units 34 are arranged atopposite ends of the die 33 on the bolster 32. These units may be thesame as the units described in the above Patent No. 3,116,780 of January7, 1964. However, it is advantageous to mount them on the upright endwalls of the female die 33 by suitable means, such as the bolts 35.

7 Each unit 34 comprises a supporting body 36 in which is provided areversible hydraulic piston and cylinder assemblage 37 comprising a rowof cylinders 38 in which are pistons 39 having piston rods 40. The endsof the rods 40 are secured to a fixed end plate 41 of the body 36through which the bolts 35 extend and secure the unit to the female die33. The cylinders 38 preferably are formed in a common block, which isconnected by spacers 42 to a stretch forming head 43. The stretchforming head 43 is supported on the top of a body 36 in suitableguideways 44 for movement transversely of the die path endwise of thestock. The head 43 is shown as having complementary gripping jaws 45 andcooperable wedges 46 so arranged that when the stock is gripped betweenthe jaws and tension is applied, the jaws are drawn more firmly intogripping position. The jaws are moved to open and closed positions bymeans of a reversible piston and cylinder assemblage 47, the piston rod48 of which is connected to the jaws.

The two units may be identical with each other. They are operableindependently of each other. The manner of operation is illustrated inthe schematic diagram of FIG. 9.

The stretch heads 43 may be, if desired, arranged on elevators as in theabove Patent No. 3,116,780, particularly if the male die is carried onthe bolster. This is so that the metal can be first stretched about themale die by the stretch heads if desired, though this is not essential.When the female die is carried on the bolster and the male die on theram as illustrated, the elevators are unnecessary.

The specific details of the structure of the units 34, other than theirconnection to the die, are not a part of the present invention.

The stretch units 34 thus are adapted to grip opposite end margins of alength of stock and stretch it into a range above its elastic limitpreparatory to closure of the dies and, if desired, during closure ofthe dies.

Preferably the units are arranged with the throats of the heads 43 closeto the plane of the upper faces of the margins of the female die so thatthe heads will not have to be moved vertically during the formingoperation and can be made a part of the die itself. Thus each die beingprovided with its own stretch units particularly adapted for its use inhigh production and used in such double action press is available.

Referring next to FIG. 2, the hold down ring 30 is in the form of aframe having lateral margins 50 extending in the direction of tensioningand end margins 51 extending transversely of the direction oftensioning. In the form illustrated in FIG. 2, the under faces of thelateral margins 50 are provided with raised beads 52. Such beads areconventional and, as best illustrated in FIG. 6, are in the form ofsolid rods 53 held in place by suitable screws, not shown. These beadsare thus replaceable and may be ground off for obtaining the amount ofhold down pressure required on the margins of the sheet at differentportions therealong. Thus by adjusting the hold down pressure applied onthe hold down ring 30 by the conventional press adjustment devices 24 ofthe outer or hold down ram 6 and by modifying the beads 52 by grinding,filing, shimming, or the like, preselected frictional resistance to thedrawing or pulling in of the sheet margins gripped beneath the ring 36can be provided.

Correspondingly, the margins about the cavity of the female die areprovided with upwardly open grooves 57 which cooperate withthe bead 52so that the stock can be drawn thereinto by the beads and held fixedlyor with controlled slippage, as desired.

In the form illustrated in FIGS. 1 through 4, it is assumed that thestretch heads 43 will be maintained operable to provide yieldabletensioning force on the stock endwise of the stock preparatory to andduring die closure. For this reason, the end margins 51 of the ring 38are ground back slightly so they do not exert any pressure on the stockat the ends aligned with the gripping heads 43. Thus the gripping headstake over the maintenance of yieldable resistance to draw in of thestock endwise. The amount of draw in endwise can be controlled bycontrolling the hydraulic pressure supplied to the stretch heads. Inoperation, the stretch units 34 are operated to stretch the stock into arange above its elastic limit. The rams are started on their cycle, thehold down ram 6 first applying the hold down ring 30 to the margins ofthe stock while the stock is held under tension by the stretch units.Due to the lazy link power transmitting connections to the rams 6 and10, the ring 30 can dwell in gripping position as the ram descends tofinal position. Further downward movement of the ram 10 applies thedrawing die 31 to the stock to force it into the female die and draw itto final shape.

With this arrangement, the forming of some shapes which, due toso-called sharp character lines or abrupt changes in surface contourcannot be readily formed by prior methods and apparatus to the sharpnessrequired, can be formed readily.

Usually, as mentioned, the hold down beads 52 and the grooves 57 of thedie are such that the metal stock is not completely locked at thelateral edges but can slip and move in if the increase in tension due todie closure exceeds a predetermined amount. By grinding off the heads atdifferent places along their length, the amount of resistance to draw inat diiferent positions along the sheet relative to other portions can becontrolled.

It sometimes happens, however, that severe draw-in may be present at theends of the stock and it is desired not to maintain this draw-in by thestretch heads. In such case, a ring 58 may be substituted for the ring30. The ring 58 has lateral margins 59 and end margins 69. The onlydifference between the rings and 58 gage and grip the end margins of thestock. The margins 60 may be provided with beads 61 for engagement withthe corresponding grooves in the female die. Accordingly, the femaledie, indicated at 62, is modified to provide grooves 63 complementary tothe end beads 61. The lateral margins of the ring 58 contain heads, thesame as the lateral margins of the ring 30.

In some cases, it is not necessary to provide beads since the clampingpressure of the fiat under surface of the ring 58 at the end margins, orlateral margins may be sufiicient. The use of beads, however, givesbetter control.

When using the form of hold down ring illustrated in FIGS. 7 and 8,there is no need to maintain the tensioning pressure on the grippingheads 43 after the hold down ring 58 is in seated position. Accordingly,if desired, after the hold down ring 53 is firmly seated on the stock,the pressure in the units 34 may be released. However, it can be used tosupplement the holding effect of beads 61, so that finer variations inslippage can be obtained by varying the pressure if fluid supplied tothe stretch units.

In some cases, for high speed production, it is desirable that theoperations be controlled automatically and for this purpose, control ofthe stretch units relative to the cycling of the press can be obtainedby circuitry such as illustrated in FIG. 9. As there illustrated, thecircuitry for each unit 34 may be the same so that one only is describedin detail.

Each circuit includes a pump P driven by a motor M. The pressure side ofthe pump is connected to a solenoid operated cut-off and reversing valve64 which, in turn, is connected to the piston and cylinder assemblage 47for jaw operation. When the valve is shifted to one position it admitsfluid pressure to the assemblage 47 so as to close the jaws and whenmoved to another position it admits fluid pressure so as to open thejaws. The valve may be spring restored to a neutral position or to anopen jaw position, if desired, but, as shown, is operated by solenoids64a and 64b.

The pressure side of the pump is connected also to a suitable solenoidoperated cut-off and reversing valve 65 which is connected to thestretch forming assemblage 37. It is so operated that it can lock theassemblage 37 in any selected position, or can admit pressure fluid fortensioning the stock and, in turn, release the fluid pressure fordriving the heads relatively toward each other for releasing the stock.The valve 65 is operated by suitable solenoids 65a and 65b.

While not shown, the usual pressure regulators and like devices may beprovided between the outlet of the pump and the valve 65, for example,as indicated in the above Letters Patent 3,116,780. Details of suchspecific control elements form no part of the invention.

The solenoid 64a is operated by a limit switch 640 and the solenoid 6412by a limit switch 64d. The solenoid 65a is operated or controlled by alimit switch 650 and the solenoid 65b by a limit switch 65d.Corresponding limit switches control corresponding solenoids for thecircuit of the other unit 34 which bears in the diagram the same numbersas the one described.

In order to operate the limit switches in relation to the position ofthe hold down ram 6 and die ram 10, they may be operated by a suitablerotatable drum 67 controller driven by a pulley 68 which may beconnected to one of the driving gears of the press.

The drum control 67 is a conventional type in which sockets 67a areprovided and receive suitable pins 69 which are detaichably inserted inthe proper sockets in the drum for tripping the switches in selectedrelation to the positions of the rams. These pins are operative to tripthe switches mechanically as the pins pass preselected locations.

Various other means of operating the switches in sequence may beemployed if desired, or the sequence may be effected by manualmanipulation of the limit switches.

In some instances, it is desirable for high speed production that all ofthe operations be performed mechanically. For this purpose, themodification shown in FIG. 10 is employed.

As there illustrated, the press structure is essentially the same as thepressure structure heretofore described except for the mechanical meansfor operation of the stretch forming units. The press is shown asprovided with a bolster 70' corresponding to the bolster 32. The bolstersupports the female die 73 having a peripheral margin 74. Bolted toopposite ends of the die 73 are stretch units 75. Each unit includes astretch head 76, such as heretofore described. The stretch head 76 iscarried on an elevator 77 which has limited vertical movement to assureproper bottoming of the hold down ring, as is later described. Theelevator 77 is urged upwardly and yieldably retained in its uppermostposition by means of air or yieldable fluid pressure piston and cylinderassemblages 78, arranged at the front and rear of the press. Each headis mounted on a carriage 79 which is movable along horizontal guidewayson the top of its elevator toward and away from the path of the dies. Atthe ends of the head are upwardly open sockets 80 which have camsurfaces 81. Mounted on the hold down ram are rigid depending members 82carrying at their lower ends suitable cam members 83 which can enter thesockets 80. The members 83 have cam surfaces 84 complementary to the camsurfaces 81 of the sockets 80. The cam surfaces are arranged so that asthe members 83 are lowered by the outer or hold down ram, they cooperateto force the stretch heads 76 relatively apart for stretching the stock.Themembers 8-2 have bottoming shoulders 85 which, when the stretch headshave been moved their maximum distance apart, engage suitable shoulders86 on the upper ends of the heads 76. These shoulders are arranged sothat the heads are in the outermost stretching or tensioning positionselected at the time of bottoming of the shoulders. The outer ram 87carries a hold down ring 88 illustrated in FIG. 10. The ring 88 may havebeads 88a which, if desired, may extend about substantially the entireperiphery of the lower end of the ring. These surfaces cooperate withsurfaces on the upper margin of the female die which may be providedwith grooves 88b extending about the entire periphery of the upwardlyfacing margin of the female die for cooperation with beads 88a when suchbeads are provided. Upon lowering of the ram 87, the heads 76 are firstmoved apart to stretch the stock, after which the shoulders 85 and 86engage and move the heads 76 and their elevators 77 downwardly againstthe resistance of the restoring cylinder assemblages 78. The members 82are mounted in the ram 87 for vertical sliding movement relative theretoto extended and retracted positions and are yieldably held in extendedpositions by springs 89. This arrangmen-t provides a lost motionconnection such that when the shoulders 85 force the stretch heads 76 totheir lower-most position against stops 90, the outer or hold down ram87 can continue to descend. The stops 90 are positioned so that when theheads 76 bottom, the stock is substantially in the plane of the upperfaces of the margins of the die 73. This action brings the stock downsubstantially to the level of the upwardly facing upper margins of thefemale die 73, preferably disposing the stock against the margins whileit is held stretched. This is followed by engagement and dwell of thehold down ring 88.

Since the stretch heads 76 are not urged yieldably apart and are notpermitted to be drawn toward each other by the stock under yieldableresistance as the dies close, the jaws of the head 76 usually arereleased after the ring 88 seats and before die drawing occurs. This maybe done by any suitable limit switch arrangement operated in timedrelation to the operation of the outer ram of the press, .or manually.The inner ram, indicated at 91, carries a male die 92 cooperable withthe female die.

In operation upon lowering of the two rams 87 and 91 concurrently, theouter ram, through the members 82 and 83, moves the heads 76 relativelyapart and stretches the material. This movement continues until theshoulders and 86' engage, whereupon they move downwardly and move theheads 76 downwardly with the outer ram while the heads remain instretching position. This operation continues until the hold down ring88 seats. Thereupon the gripping jaws of the stretch heads 76 arereleased. Continued operation of the press causes the ring 88 to dwellin gripping position and the die a2 to cooperate with the female die 73to draw the stock promptly while it is still in more readily deformablecondition as a result of its immediately preceding stretching above itselastic limit.

The releasing of the jaws of the stretch units in relation to theoperation of the outer ram 87 is not shown, but it may be byconventional limit switches operated by a drum moved in timed relationto the driving of the outer ram, as hereinbefore described in connectionwith FIGS. 1 through 9.

In order to restore the heads to their innermost positions for insertingthe stock as they are released by the members 83, suitable air operatedpiston and cylinder assemblages 93 are connected to the carriage of theheads, the air therein being compressed by movement of the unitsrelatively apart, so that upon release of the units, the air re-expandsand drives the heads inwardly toward their original loading or startingposition. If desired, compression springs may be used in the assemblages93 instead of air for this purpose.

It is apparent that, in accordance with the present invention, the stockis first tensioned into a range above its elastic limit preparatory toits being formed by cooperation of the companion drawing dies, andpreferably while it is out of contact with either die. While thusstretched, it is engaged by the hold down ring, in the first instance,at its lateral margins while held under yieldable tension at its endmargins by the stretch heads, the lateral margins being thusconstrained, to the degree selected, from inward movement by the holddown and the end margins by the stretch heads. While still in thisreadily deformable condition and so controlled, the dies are closeddrawing the piece into a finished article. The usual knock-out pins andthe like may be provided in the female die for releasing the articletherefrom. Such are conventional and form no part of the presentinvention.

In both forms of the structure, as mentioned, the stock may be held atall margins by the hold down ring after once stretched, the jaws of thestretch heads being released after seating of the ring so thatthereafter all control of the inward movement of the margins of thestock is by virtue of the hold down ring.

Having thus described our. invention, we claim:

1. In a combined stretch forming and die drawing apparatus,

a ram member,

a bed member,

power means for moving the members relatively toward and away from eachother,

complementary male and female drawing dies carried by the members,respectively, for movement thereby to closed and open positions, fordrawing sheet metal stock therebetween upon closure,

power operated stretch forming means including stock gripping heads attwo opposite sides of the path of the dies for gripping two oppositemargins of the stock and for stretching the stock endwise prior tomovement of the dies to closed position,

power driven restraining means at the other two opposite limits of thedie path and operable, independently of the dies and stretch formingmeans, after the stretching operation and prior to said movement of thedies to closed position for gripping opposite faces of the stock at thelateral margins and for holding the margins gripped with predeterminedholding pressure, during movement of the dies to closed position, forcontrolling the lateral draw in of the stock by the dies during dieclosure.

2. An apparatus according to claim 1 wherein the restraining meansinclude power means operable to cause the restraining means to engagethe stock with sufiicient force to hold the margins fixedly in theposition in which gripped.

3. An apparatus according to claim 1 wherein additional power operatedrestraining means are provided at the said two margins gripped by thestretch forming means, and are operable, after stretching of the stockby the stretch forming means, to engage the stock and resist draw in ofthe stock endwise by the dies.

4. An apparatus according to claim 1 wherein means are provided forreleasing the stretch forming means after the additional power operatedrestraining means are rendered operative.

5. An apparatus according to claim 1 wherein the stretch forming meansare operable to apply yieldable tensioning force to the stock endwise ofthe stock while the power operated restraining means are operative.

6. An apparatus according to claim 1 wherein the stretch forming meansare carried on one of the dies.

7. An apparatus according to claim 1 wherein the stretch forming meansare carried by one of the members, and means connect the other member tothe stretch forming means so as to move the stretch forming headsrelatively apart as the members move toward each other.

8. An apparatus according to claim 1 wherein the stretch forming meansare arranged to suspend the stock between, and out of contact, with thedies, and to stretch the stock, while the dies are open, and therestraining means are operable to engage margins of the stock while thestock is so suspended.

9. The method of combined stretch and draw die forming of sheet metalstock, and comprising applying yieldable stretching force to two endmargins of a length of stock to stretch the stock endwise and therebyrender it more readily formable while leaving the lateral margins of thestock free to draw inwardly of the stock transversely of the stock, thenafter stretching the stock and while it is thus more readily formable,gripping at least the lateral margins of the stock and thereby resistingdraw in of the lateral margins toward each other, and, while thusresisting lateral draw in, promptly drawing the stock between matchingdrawing dies.

10. The method according to claim 9 wherein the forces resisting draw inof the stock by the dies is applied to all margins of the stock prior todrawing by cooperation of the dies and said forces are maintained duringthe drawing of the stock by coaction of the dies.

11. The method of drawing sheet metal stock comprising applyingstretching force to the opposite end margins of a length of stock tostretch the stock endwise and thereby render it more readily formablewhile leaving the lateral margins of the stock free to draw inwardly ofthe stock transversely of the stock, then after stretching the stock,and while maintaining the application of said stretching force, grippingthe lateral margins of the stock, thereby causing forces resisting drawin of the lateral margins toward each other, and while the stock is thusin more readily deformable condition, drawing the stock within saidmargins between matching drawing dies while all of said margins aresubjected to their said associated ones of said forces.

12. The method according to claim 11 wherein resisting forces areapplied to all margins while said stretch forming forces are still beingapplied but subsequent to the stretching, the stretch forming forces arethen released and the resisting forces maintained, after which the stockis drawn.

13. The method according to claim 11 wherein the stretching force is ayieldable force, and the end margins ?re restrained from draw in by theyieldable stretching orce.

14. The method according to claim 11 wherein additional force resistingdraw in is applied at the end margins while the stretching force ismaintained, and upon ap-- plication of the additional force, thestretching force is released.

15. The method of forming sheet metal stock comprising, applyingstretching force to opposite end margins of a sheet of stock to stretchit endwise sufiicient to render it more readily drawable while leavingthe lateral margins of the stock free to draw inwardly transversely ofthe stock, then releasing the stretching force, and promptly, while thestock remains in the more readily drawable condition, first applying tothe stock margins, in a direction generally normal to their faces,restraining forces for frictionally resisting draw in of the stock bythe dies, and then drawing the stock by the dies.

16. The method of combined stretch and draw die forming of sheet metalstock, comprising applying stretching force to two opposite end marginsof a length of stock and thereby stretching the stock endwise beyond itselastic limit to render it more readily formable while leaving thelateral margins of the stock free to draw inwardly transversely of thestock and while the stock is clear of the article forming surfaces ofmatching drawing dies by which it is to be drawn, then, after thusstretching the stock and while it is in a more readily formableposition, gripping at least portions of the lateral margins of the stockand thereby resisting the draw-in of the lateral margins toward eachother and, while thus resisting lateral graw-in, promptly drawing thestock by closure of the res.

17. An apparatus according to claim 1 wherein the stretch forming meansare arranged to suspend the stock between, and out of contact, with thedies, and to stretch the stock, while the dies are open, and therestraining means are operable to engage margins of the stock and applyholding force thereto prior to drawing of the stock by cooperation ofthe dies with the stock.

18. An apparatus according to claim 1 wherein the stretch forming meansare arranged to suspend the stock between, and out of contact, with thedies, and to stretch the stock, while the dies are open, and therestraining means are operable to engage margins of the stock and applyholding force thereto prior to the dies becoming fully closed.

References Cited by the Examiner UNITED STATES PATENTS 2,002,097 5/ 1935Peterson 72297 2,302,953 11/1942 Pocock 72-302 3,113,607 12/1963 Maize72296 CHARLES W. LANHAM, Primary Examiner. R. IQ. GREFE, AssistantExaminer.

1. IN A COMBINED STRETCH FORMING AND DIE DRAWING APPARATUS, A RAMMEMBER, A BED MEMBER, POWER MEANS FOR MOVING THE MEMBERS RELATIVELYTOWARD AND AWAY FROM EACH OTHER, COMPLEMENTARY MALE AND FEMALE DRAWINGDIES CARRIED BY THE MEMBERS, RESPECTIVELY, FOR MOVEMENT THEREBY TOCLOSED AND OPEN POSITIONS, FOR DRAWING SHEET METAL STOCK THEREBETWEENUPON CLOSURE, POWER OPERATED STRETCH FORMING MEANS INCLUDING STOCKGRIPPING HEADS AT TWO OPPOSITE SIDES OF THE PATH OF THE DIES FORGRIPPING TWO OPPOSITE MARGINS OF THE STOCK AND FOR STRETCHING THE STOCKENDWISE PRIOR TO MOVEMENT OF THE DIES TO CLOSED POSITION, POWER DRIVENRESTRAINING MEANS AT THE OTHER TWO OPPOSITE LIMITS OF THE DIE PATH ANDOPERABLE, INDEPENDENTLY OF THE DIES AND STRETCH FORMING MEANS, AFTER THESTRETCHING OPERATION AND PRIOR TO SAID MOVEMENT OF THE DIES TO CLOSEDPOSITION FOR GRIPPING OPPOSITE FACES OF THE STOCK AT THE LATERAL MARGINSAND FOR HOLDING THE MARGINS GRIPPED WITH PREDETERMINED HOLDING PRESSURE,DURING MOVEMENT OF THE DIES TO CLOSED POSITION, FOR CONTROLLING THELATERAL DRAW IN OF THE STOCK BY THE DIES DURING DIE CLOSURE.